1. Field of the invention
The present invention relates to a detecting portion and an airway adaptor which is fitted to the detecting portion and used for letting pass respiratory gas in, for example, a capnometer for measuring the concentration of carbon dioxide gas contained in expiratory gas.
2. Related art
When the concentration of carbon dioxide gas contained in expiratory gas is measured, the following steps are followed; namely, using an optical detector, for example, PbSe as an infrared radiation detector, causing the respiratory gas to pass through a cylindrical transparent plastic airway adaptor, and irradiating the respiratory gas with infrared radiations from a light source so as to detect, by means of the detector, voltage corresponding to the absorption of light resulting from the expiratory carbon dioxide gas.
FIGS. 12 and 13 are schematic views of an example of a conventional capnometer. In FIGS. 12 and 13, one end 1a of an airway adaptor 1 which is substantially cylindrical and used for letting pass a respiratory gas therethrough is a connection end to be held in a patient's mouth, whereas the other end 1b is an open end communicating with the atmosphere. The intermediate portion of the airway adaptor 1 is square in cross section. Further, coaxial circular windows 1c, 1d are formed in two facing sides of the intermediate portion of the airway adaptor 1, respectively. The intermediate portion of the airway adaptor 1 is detachable from a detecting portion 2.
The detecting portion 2 is in the form of a substantially square pillar, and its intermediate portion is provided with a U-shaped cutaway portion 2e into which the intermediate portion of the airway adaptor 1 is fitted. The facing two sides of the cutaway portion 2e are in contact with the respective windows 1c, 1d of the airway adaptor 1. A light source 3 for emitting infrared radiations is placed on one side of the cutaway portion 2e of the detecting portion 2, whereas a radiation interrupter 5 which is driven to rotate by a motor 4 is situated on the other side. There are also formed a plurality of coaxial light transmitting holes for making light emitted from the light source continuously intermittent in the radiation interrupter 5.
A filter 6 for passing light only having a wavelength to be absorbed by carbon dioxide gas, and a light detector 7 as an infrared radiation detector are disposed in a direction opposite to the light source 3 with respect to the radiation interrupter 5. The light detector 7 is connected via a lead wire 8 to a monitor body 9. In this case, the intermediate portion of the airway adaptor 1 is detachable from the detecting portion 2 via a pair of ball plungers 10 provided in the detecting portion 2.
In the conventional capnometer thus constructed, the light emitted from the light source 3 passes through the window 1c and respiratory gas in the airway adaptor 1, whereas the light emitted through the window 1d is made incident as intermittent light on the optical detector 7 by the radiation interrupter 5 via the filter 6. Thus the light intensity corresponding to the concentration of carbon dioxide gas is detected by the optical detector 7, and an output signal of the optical detector 7 is input to the monitor body 9 before being displayed as the concentration of the carbon dioxide gas.
The aforementioned conventional capnometer employs an expensive PbSe as an infrared radiation detector and because PbSe greatly drifts with temperature variations though response speed is high, light has to be detected while it is made continuously intermittent. For this reason, the conventional capnometer needs the radiation interrupter 5 and the motor 4 for driving the interrupter, so that it tends to become not only large in size but also costly.
Further, a great deal of power is essential to driving the motor 4 to rotate, which results in the necessity of providing a large power supply for the monitor body 9. In addition, there has to be a circuit for demodulating the intermittent detected signal in the monitor body 9 and this also makes it impossible to decrease the size of the monitor body 9. In view of easy-to-use, it has become necessary to use the detecting portion 2 equipped with the airway adaptor 1 separately from the monitor body 9 connected to the former via a lead wire 8.
In a case where the detecting portion 2 equipped with the airway adaptor 1 is used so that it is placed between a mask for covering the mouth of a patient and an air bag fitted to the other end at the time of, for example, ventilation, it will not be possible for a helper to observe the patient's condition such as his complexion simultaneously with the display portion of the concentration of carbon dioxide gas as the detecting portion 2 is separated from the monitor body 9. The trouble is that the helper will have to turn his gaze at all times. Moreover, there has been the possibility that the monitor body 9 may drop or otherwise the lead wire 8 for connecting the detecting portion 2 and the monitor body 9 together may be disconnected during the time a patient is moved on a stretcher since the detecting portion 2 and the monitor body 9 are separated from each other.
Therefore when the concentration of carbon dioxide gas is measured, a helper must supply air while watching the display portion of the monitor body 9. In other words, the monitor body 9 is desired to be integral with the detecting portion 2. However, the problem is that operability will be impaired if the monitor body 9 is fitted with the detecting portion 2 because not only the detecting portion 2 but also the monitor body 9 is large-sized and heavy as set forth above.
The airway adaptor 1 can be made disposable when it is contaminated. However, the airway adaptor 1 has conventionally been fixed to the detecting portion 2 with ball plungers 10. Consequently, the airway adaptor 1 may be set unsatisfactorily without being properly fitted into the cutaway portion 2e of the detecting portion 2. In this case, the light intensity may decrease, which may also deteriorate the S/N precision, thus bringing about an erroneous diagnosis. Since the ball plungers 10 fitted to the detecting portion 2 press the intermediate portion of the airway adaptor 1, the counter force acts in the same direction as that of the optical axis, increases the distance between the light source 3 and the optical detector 7 and decreases the light intensity, so that precision may deteriorate. In order to solve this problem, the rigidity of the detecting portion 2 must be increased.